Process for preparing iminodiacetonitrile

Abstract

Iminodiacetonitrile is prepared by a batch process comprising reacting hexamethylenetetramine and HCN in an aqueous medium in the presence of a strong acid at a pH of 5.5-6.5 while maintaining an excess of HCN in the reaction mixture.

I claim: 
     
       1. In a batch process for preparing iminodiacetonitrile comprising reacting hexamethylenetetramine and HCN in an acidic aqueous medium and recovering the iminodiacetonitrile, the improvement comprising: a. forming a first solution by admixing anhydrous HCN and a second solution having a pH of 5-7, a temperature of 0°-50° C, and consisting essentially of water, a strong acid, and hexamethylenetetramine, the HCN present in the first solution being 6-50% of that used per batch and the hexamethylenetetramine present in the first solution being 0.5-45% of that used per batch, the mole ratio of HCN to hexamethylenetetramine in the first solution being greater than 6:1 and less than 12:1;   b. forming a third solution by simultaneously adding to the first solution: (i) anhydrous HCN; and (ii) a fourth solution consisting essentially of water, hexamethylenetetramine, and the strong acid while maintaining the temperature of the resulting third solution at 10°-75° C, the fourth solution containing one mole of hexamethylenetetramine per equivalent of the acid, the anhydrous HCN and the fourth solution being added at rates such that: (I) the mole ratio of HCN to hexamethylenetetramine in the third solution is at least 6:1; and (II) the pH of the third solution is 5.5-6.5;   c. adjusting the temperature of the third solution to 30°-70° C if it is not already within this temperature range; and   d. forming iminodiacetonitrile by adding to the third solution over a period of time effective for forming iminodiacetonitrile an amount of the strong acid effective for maintaining the pH of the resulting mixture at 5.5-6.5 while maintaining the temperature thereof at 30°-70° C.   
     
     
       2. The process of claim 1 in which the temperature of the first solution is maintained at 10°-65° C. 
     
     
       3. The process of claim 1 in which the temperature of the third solution is maintained at 30°-70° C. 
     
     
       4. The process of claim 1 in which the strong acid is sulfuric acid. 
     
     
       5. The process of claim 1 in which HCN and the second solution are admixed to form the first solution while maintaining the temperature of the resulting first solution at 25°-65° C. 
     
     
       6. The process of claim 1 in which HCN and the second solution are admixed at rates to provide 6.5-8 moles of HCN per mole of hexamethylenetetramine in the resulting first solution. 
     
     
       7. The process of claim 1 in which the mole ratio of HCN to hexamethylenetetramine in the third solution is maintained within the range of 6.1-7:1.